I settled on making it terrestrial, so here we go.
Trying to get a feel for how this creature would move - I referenced a lot of horses for the gait (thank goodness for Edweard Muybridge), because I felt like it would be more unusual for this thing to be agile rather than slow and lumbering like the legs suggest. Also experimenting with senses - I've decided that it won't have eyes, so it needs some other way of experiencing the world. The tendril-barbel-things looked too distracting, but I finally settled on a head shape while I was at it so it's not entirely a waste.
Applying the final head shape (which does actually have significant angles and curves, contrary to my original thinking). The body works better short rather than long, but I'm struggling to get the back to slope as much as I want it to. Still not sure about texture, I went forward with the furred one just to get things done but I keep looking back to the hairless one. I also finalised the way the legs work - yes, it's a stick diagram, but it does the job.
I went into Photoshop to mess with colours - which I'm not entirely sure I'm supposed to do, but what the hey. My favourites are currently #2, #3 and #8, but they've been changing all day so I'll sleep on it before making any actual decision.